Adsorption arsenic

For a reconstmcted surface, the effect of an adsorbate can be to provide a more bulk-like enviromnent for the outemiost layer of substrate atoms, thereby lifting the reconstmction. An example of this is As adsorbed onto Si(l 11)-(7 X 7) [37]. Arsenic atoms have one less valence electron than Si. Thus, if an As atom were to replace each outemiost Si atom in the bulk-temiinated stmcture, a smooth surface with no impaired electrons would be produced, with a second layer consisting of Si atoms in their bulk positions. Arsenic adsorption has, in fact, been found to remove the reconstmction and fomi a Si(l 11)-(1 x l)-As stmcture. This surface has a particularly high stability due to the absence of dangling bonds. 

Adsorption, which utilizes the ability of a solid adsorbent to adsorb specific components from a gaseous or a liquid solution onto its surface. Examples of adsorption include the use of granular activated carbon for the removal of ben-zene/toluene/xylene mixtures from underground water, the separation of ketones from aqueous wastes of an oil refinery, aad the recovery of organic solvents from the exhaust gases of polymer manufacturing facilities. Other examples include the use of activated alumina to adsorb fluorides and arsenic from metal-finishing emissions. 

In addition to effects on the concentration of anions, the redox potential can affect the oxidation state and solubility of the metal ion directly. The most important examples of this are the dissolution of iron and manganese under reducing conditions. The oxidized forms of these elements (Fe(III) and Mn(IV)) form very insoluble oxides and hydroxides, while the reduced forms (Fe(II) and Mn(II)) are orders of magnitude more soluble (in the absence of S( — II)). The oxidation or reduction of the metals, which can occur fairly rapidly at oxic-anoxic interfaces, has an important "domino" effect on the distribution of many other metals in the system due to the importance of iron and manganese oxides in adsorption reactions. In an interesting example of this, it has been suggested that arsenate accumulates in the upper, oxidized layers of some sediments by diffusion of As(III), Fe(II), and Mn(II) from the deeper, reduced zones. In the aerobic zone, the cations are oxidized by oxygen, and precipitate. The solids can then oxidize, as As(III) to As(V), which is subsequently immobilized by sorption onto other Fe or Mn oxyhydroxide particles (Takamatsu et al, 1985). 

On the surface of metal electrodes, one also hnds almost always some kind or other of adsorbed oxygen or phase oxide layer produced by interaction with the surrounding air (air-oxidized electrodes). The adsorption of foreign matter on an electrode surface as a rule leads to a lower catalytic activity. In some cases this effect may be very pronounced. For instance, the adsorption of mercury ions, arsenic compounds, or carbon monoxide on platinum electrodes leads to a strong decrease (and sometimes total suppression) of their catalytic activity toward many reactions. These substances then are spoken of as catalyst poisons. The reasons for retardation of a reaction by such poisons most often reside in an adsorptive displacement of the reaction components from the electrode surface by adsorption of the foreign species. 

Herteto E, Rodes A, Perez JM, Feliu JM, Aldaz A. 1995d. CO adsorption and oxidation on Pt(lll) electrodes modified by irreversibly adsorbed arsenic in sulfimc-acid medium— Comparison with bismuth-modified electrodes. J Electroanal Chem 393 87-96. 

Mukherjee, S. and Kumar, S., Adsorptive uptake of arsenic(V) from water by aquatic fern Salvinia natans, Journal of Water Supply Research and Technology—Aqua, 54 (1), 47-53, 2005. 

Ashokkumar et al. [128] have reported the sonochemical conversion of As(III) to As(V) in an aqueous solution as a process for the removal of arsenic in contaminated water. A very interesting pH independent sonochemical conversion of arsenic (III) to arsenic (V), besides its precipitation as sulphide in aqueous solutions, in the pH range 5 to 9, and subsequent adsorption on coagulants such as Fe(OH)3 and Al(OH)3 has also been reported [129] from this laboratory. 

The heat sensitivity (above) may explain the explosions which occur on contact of many readily oxidisable materials with this powerful oxidant. Such materials include ammonia, potassium arsenic, antimony sulfur, charcoal (adsorptive... 

Arsenate is readily adsorbed to Fe, Mn and Al hydrous oxides similarly to phosphorus. Arsenate adsorption is primarily chemisorption onto positively charged oxides. Sorption decreases with increasing pH. Phosphate competes with arsenate sorption, while Cl, N03 and S04 do not significantly suppress arsenate sorption. Hydroxide is the most effective extractant for desorption of As species (arsenate) from oxide (goethite and amorphous Fe oxide) surfaces, while 0.5 M P04 is an extractant for arsenite desorption at low pH (Jackson and Miller, 2000). 

Frost R.R., Griffin R.A. Effect of pH on adsorption of arsenic and selenium from landfill leachate by clay minerals. Soil Sci Soc Am J 1977 41 53-57. 

Arai Y, Elzinga EJ, Sparks DL (2001) X-ray absorption spettroscopy investigation of arsenite and arsenate adsorption on the aluminium oxide-water interface J Colloid Interf Sci 235 80-88... 

Frost RR, Griffin RA (1977) Effect of pH on adsorption of As and selenium from land fill leachate by clay minerals. Soil Sci Soc Am J 41 53—57 Goh K-H, Lym TT (2005) Arsenic fractionation in a fine soil fraction and influence of various anions on its mobility in the sub surface environment. Appl Geochem 20 229-239... 

Hongshao Z, Stanforth R (2001) Competitive adsorption of phosphate and arsenate ongoethite. Environ Sci Technol 35 4753—4757 Hsia TH, Lo SL, Lin CF, Lee DY (1994) Characterization of arsenate adsorption on hydrous iron oxide using chemical and physical methods. Colloid Surface A 85 1-7... 

Kampf N, Scheinost AC, Schultze DG (2000) Oxides minerals. In Sumner ME (ed) Handbook of soil science, CRC Press, Boca Raton (FL), F125-F168 Jain A, Loeppert RH (2000) Effect of competing anions on the adsorption of arsenate and arsenite by ferrihydrite. J Environ Qual 29 1422-1430 Jain A, Raven KP, Loeppert RH (1999) Arsenite and arsenate adsorption on ferrihydrite surface charge reduction and net OH release stoichiometry. Environ Sci Technol 33 1179-1184... 

Lafferty BJ, Loeppert RH (2005) Methyl arsenic adsorption and desorption be-hatior on iron oxides. Environ Sci Technol 39 2120—2127 Le XC (2002) Arsenic speciation in the environment and humans. In Frankenberger WT Jr (ed) Environmental chemistry of arsenic. Marcel Dekker, Inc. New York, pp 95-116... 

Liu F, De Cristofaro A, Violante A (2001) Effect of pH phosphate and oxalate on the adsorption/desorption of arsenate on/from goethite. Soil Sci 166 197-208 Livesey NT, Huang PM (1981) Adsorption of arsenate by soils and its relation to selected properties and anions. Soil Sci 131 88-94 Manceau A (1995) The mechanism of anion adsorption on iron oxides Evidence for the bonding of arsenate tetrahedra on free Fe(0, OH)6 edges. Geochim Cosmochim Acta 59 3647-3653. 

Manning BA, Goldberg S (1997a) Adsorption and stability of arsenic (III) at the clay mineral-water interface. Environ Sci Technol 31 2005-2011 Manning BA, Goldberg S (1997b) Arsenic(III) and arsenic(V) adsorption on three California soils. Soil Sci 162 886-895... 

Martin M, Violante A, Barberis E (2007a) Fate of arsenite and arsenate in flooded and not flooded soils of South West Bangladesh irrigated with arsenic contaminated water. J Environ Sci Health, Part A 42 1775-1783 Martin M, Violante A, Barberis E (2007b) Comparing surface interaction of arsenite and arsenate on soil colloids I Adsorption. Soil Sci Soc Am J (submitted)... 

Pigna M, Colombo C, Violante A (2003) Competitive sorption of arsenate and phosphate on synthetic hematites (in Italian). Proceedings XXI Congress of Societa Italiana Chimica Agraria SICA (Ancona), pp 70-76 Quirk JP (1955) Significance of surface area calculated from water vapour sorption isotherms by use of the B. E. T. equation. Soil Sci 80 423-430 Rancourt DG, Fortin D, Pichler T, Lamarche G (2001) Mineralogical characterization of a natural As-rich hydrous ferric oxide coprecipitate formed by mining hydrothermal fluids and seawater. Am Mineral 86 834-851 Raven K, Jain A, Loeppert, RH (1998) Arsenite and arsenate adsorption on ferrihydrite kinetics, equilibrium, and adsorption envelopes. Environ Sci Technol 32 344-349... 

Roy WR, Hassett JJ, Griffin RA (1986) Competitive coefficient for the adsorption of arsenate, molybdate, and phosphate mixtures by soils. Soil Sci Soc Am J 50 1176-1182... 

Sun X, Doner, HE (1996) An investigation of arsenate and arsenite bonding structures on goethite by FTIR. Soil Sci 161 865-872 Sun X, Doner HE (1998) Adsorption and oxidation of arsenite on goethite. Soil Sci 163 278-287... 

Violante A, Krishnamurti GSR, Pigna M (2008) Mobility of trace elements in soil environments. In Violante A, Huang PM and Gadd G (eds) Wiley-JUPAC series on biophysico-chemical processes of metals and metalloids in soil environments. John Wiley Sons, Hoboken, USA Waltham AC, Eick MJ (2002) Kinetic of arsenic adsorption on goethite in the presence of sorbed silicic acid. Soil Sci Soc Am J 66 818-825 Waychunas GA, Fuller CC, Rea BA, Davis J (1996) Wide angle X-ray scattering (WAXS) study of two-line ferrihydrite structure Effect of arsenate sorption and counterion variation and comparison with EXAFS results. Geochim Cos-mochim Acta 60 1765-1781... 

Haywood and Riley [14] have described a spectrophotometric method for the determination of arsenic in seawater. Adsorption colloid flotation has been employed to separate phosphate and arsenate from seawater [15]. These two anions, in 500 ml filtered seawater, are brought to the surface in less than 5 min, by use of ferric hydroxide (added as 0.1 M FeC 2 ml) as collector, at pH 4, in the presence of sodium dodecyl sulfate [added as 0.05% ethanolic solution (4 ml)] and a stream of nitrogen (15 ml/minutes). The foam is then removed and phosphate and arsenate are determined spectrophotometrically [16]. Recoveries of arsenate and arsenite exceeding 90% were obtained by this procedure. 

Yoshimura et al. [193] carried out microdeterminations of phosphate by gel-phase colorimetry with molybdenum blue. In this method phosphate reacted with molybdate in acidic conditions to produce 12-phosphomolybdate. The blue species of phosphomolybdate were reduced by ascorbic acid in the presence of antimonyl ions and adsorbed on to Sephadex G-25 gel beads. Attenuation at 836 and 416 nm (adsorption maximum and minimum wavelengths) was measured, and the difference was used to determine trace levels of phosphate. The effect of nitrate, sulfate, silicic acid, arsenate, aluminium, titanium, iron, manganese, copper, and humic acid on the determination were examined. 

Hering, J.G., P.Y. Chen, and J.A. Wilkie. 1997. Arsenic removal from drinking-water by coagulation the role of adsorption and effects of source water composition. Pages 369-381 in C.O. Abernathy, R.L. Calderon, and W.R. Chappell (eds.). Arsenic. Exposure and Health Effects. Chapman Hall, London. 

Matsunaga, H., Yokoyama, T., Eldridge, R.J., Bolto, B.A. 1996. Adsorption characteristics of arsenic(lll) and arsenic(V) on iron(lll)-loaded chelating resin having lysine-Na,Na-diacetic acid moiety. Reactive and Functional Polymers, 29, 167-174. 

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